The present invention relates generally to motion sensors for monitoring the activity of a body in motion. More particularly, the invention relates to apparatus, systems and methods by which translational or rotational motion may be suppressed from any general motion signal leaving only a rotational or translational component.
Motion sensors have been applied to a plethora of applications, one of the most important of which being research instruments for a variety of medical studies concerned with the human body. Although the present invention may be described with respect to human activity monitors, or actigraphs, it will be appreciated that the motion sensor described herein is in no way intended to be limited to such an application. In fact, it will be understood that this new type of motion sensor may be applied to any application which may necessitate the suppression of the translational or rotational motion from a general motion signal leaving only a rotational or translational component.
The observation of body movement can provide much information useful to physicians and researchers. For example, by observing movement in a subject, the occurrence and length of natural phenomenon, such as wakefulness, rest, and sleep can be determined. By observing the nature of a subject's movement, the occurrence and severity of disorders and the effects of drugs or other therapy can be assessed. In many cases quantification of the subject's movement is preferred so that the movement pattern of one subject can be compared with the movement pattern of others.
Direct visual observations of body movement are labor intensive, time consuming and tedious. Moreover, direct visual observations provide only a limited range of qualitative information, such as subjective descriptions of a subject's visually perceptible movements. Little, if any, quantification in readily comparable values, such as degree, strength, and/or violence of a subject's activity, and no information, either qualitative or quantitative, of a subject's visually imperceptible movements is obtained. Furthermore, the value of qualitative information obtained by directly observing a subject is subject to question as such observations themselves may cause the subject to become conscious of and thereby alter his or her movements.
Activity monitors, and in particular, actigraphs have been developed for observing and quantifying certain aspects of movements without the involvement of an observer. In its earliest manifestation, the actigraph was primarily a wrist worn sleep research tool, and much of modern actigraph design philosophy has evolved from this application. Today, however, actigraphs are frequently used in other research which involves hyperactivity, nocturnal tremors, circadian behavior (i.e. shift work) and Parkinson's Disease.
However, such actigraphs had disadvantages which limited their usefulness. For example, it was realized that measurement of human activity could not be accomplished if the subject was moving on a platform which was itself moving relative to the earth. Consequently, actigraphs could not be utilized effectively on a human involved in driving, flying, boating or riding on a train for example. In particular, it was discovered, at least in so far as road vehicles are concerned, that frequency range and statistics were not sufficiently different from human characteristics to allow an actigraph to separate two overlapping signals. Furthermore, it was found that road vehicle motion was found to be 10 to 100 times greater in amplitude than that produced by a riding human.
In recent years the need for a new type of actigraph capable of sensing human activity in a moving vehicle reached a new level of importance as several independent industries have become interested at the same time. For example, sleep aboard military aircraft became an important topic because transporting combat soldiers during a crisis requiring urgent deployment often requires rest/sleep onboard the aircraft. Perhaps most importantly, the Federal Highway Administration began inquiring about technology that could determine how well a truck driver sleeps in a truck berth under various scenarios. Such as, while the truck is idling, as in the case with a single crew member and while the truck is moving, as in the case with a two man crew. Others had now become interested as well primarily due to the fact that effectiveness and personal safety are determined to a great extent upon an individual's sleep quality and duration.
In view of the afore-mentioned needs and the shortcomings of the prior art, it is therefore a general object of the present invention to provide a new type of motion sensor for monitoring the activity of a body in motion.
It is another object of the present invention to provide an apparatus, system and method by which translational or rotational motion may be suppressed from any general motion signal leaving only a rotational or translational component.
Still another object of the present invention is to provide a motion sensor capable of sensing human activity in a moving vehicle.
Yet another object of the present invention is to provide a motion sensor capable of assessing sleep and performance of humans subject to long term mechanical vibrations in the work place.
Still yet another object of the present invention is to provide a motion sensor capable of recording short duration time records of important movements.
These and other objects, features and advantages of the present invention will be clearly understood through a consideration of the following detailed description.